Germanium-on-silicon mid-infrared grating couplers with low-reflectivity inverse taper excitation Academic Article uri icon

  • Overview
  • Research
  • Identity
  • Additional Document Info
  • View All


  • A broad transparency range of its constituent materials and compatibility with standard fabrication processes make germanium-on-silicon (Ge-on-Si) an excellent platform for the realization of mid-infrared photonic circuits. However, the comparatively large Ge waveguide thickness and its moderate refractive index contrast with the Si substrate hinder the implementation of efficient fiber-chip grating couplers. We report for the first time, to the best of our knowledge, a single-etch Ge-on-Si grating coupler with an inversely tapered access stage, operating at a 3.8 μm wavelength. Optimized grating excitation yields a coupling efficiency of -11  dB (7.9%), the highest value reported for a mid-infrared Ge-on-Si grating coupler, with reflectivity below -15  dB (3.2%). The large periodicity of our higher-order grating design substantially relaxes the fabrication constraints. We also demonstrate that a focusing geometry allows a 10-fold reduction in inverse taper length, from 500 to 50 μm.


  • Alonso-Ramos, Carlos
  • Nedeljkovic, Milos
  • Benedikovic, Daniel
  • Penadés, Jordi Soler
  • Littlejohns, Callum G
  • Khokhar, Ali Z
  • Pérez-Galacho, Diego
  • Vivien, Laurent
  • Cheben, Pavel
  • Mashanovich, Goran Z

publication date

  • September 15, 2016